Carrier particles have been used for various electrophotographic processes. The cascade and the magnetic brush are the principal electrophotographic processes in current use which employ carrier particles.
The cascade process is relatively slow; however, it has an advantage in that the materials employed are inherently less expensive than those employed in the magnetic brush process. The magnetic brush process has an advantage in that it reduces the restriction on copying speed associated with the cascade process, and therefore with the magnetic brush process it is possible to copy more rapidly.
In both the brush and cascade processes the development carrier particles are mixed with toner particles to form a mixture of small toner particles and relatively larger carrier particles.
The carrier particles are coated with a material such as a fluorocarbon. The coating promotes electrostatic adhesion of the toner particles to the carrier particles. When a fluorocarbon coating is used the coated carrier particles are cured by heating them to temperatures generally less than about 425.degree. C.
Since the carrier particles lose their effectiveness if the coating spalls, the life of the carrier particles may be limited by the adhesion of the coating. Spalling of the coating from the carrier particle core can be increased in the magnetic brush process by both increasing the density of the carrier particles, and by the continued agitation of the particles. This increase in density and continued agitation is necessary to assure that the carrier particles are coated by the toner particles and that the toner and carrier particles do not settle and separate.
In the magnetic brush process the magnetic character of the carrier particle core determines the character of the magnetic brush; therefore the magnetic properties of the carrier particle core determines the response to the magnetic field and limits both the resolution and the copying speed. Among the ferromagnetic materials currently used for carrier particle cores are iron, low carbon steels, silicon steels, magnetic oxides, and other iron base alloys. Providing a carrier particle core with improved magnetic properties could increase both the resolution and operating speed of the magnetic brush process.
It is an object of the present invention to provide a carrier particle which will be more responsive to magnetic fields.
It is another object of the present invention to provide a carrier particle core which is more responsive to magnetic fields and therefore produces a magnetic brush which when used in an electrostatic copying process gives enhanced resolution.
It is still another object of the present invention to provide a carrier particle that will require less agitation to prevent settling.